To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition rating of 80 (MS+). This is an important factor, as coins in better condition tend to fetch higher prices.

2. Starting Price: The starting price is 400 euros. This is the baseline for the auction.

3. Sales History: The coin has been auctioned 154 times, of which it has sold 148 times. This indicates good demand and a history of successful sales.

4. Previous Prices: By looking at previous hammer prices for coins with similar conditions, we can see that hammer prices have varied. For example, in recent auctions, coins with conditions ranging from 85 to 90 have reached hammer prices between 320 and 400 euros.

5. Recent Trends: In the most recent auctions, hammer prices for coins with similar conditions have been in the range of 360 to 450 euros.

Based on these factors, an estimated maximum purchase price for this coin could be between 450 and 500 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate. However, since the starting price is 400 euros, it is likely that buyers will be willing to bid beyond this price, especially if there is interest in the coin.

Therefore, a reasonable maximum purchase price could be 450 euros.